Electrical Clearance in Substation

 Minimum Clearance in Substation:

Voltage	Highest Voltage	Lighting Impulse Level (Kvp)	Switching Impulse Level (Kvp)	Minimum Clearance		Safety Clearance(Mt)	Ground Clearance(Mt)
				Phase-Earth	Phase-Phase
11KV	12KV	70		0.178	0.229	2.600	3.700
33KV	36KV	170		0.320	0.320	2.800	3.700
132KV	145KV	550		1.100	1.100	3.700	4.600
		650		1.100	1.100	2.700	4.600
220KV	245KV	950		1.900	1.900	4.300	5.500
		1050		1.900	1.900	4.300	5.500
400KV	420KV	1425	1050(P-E)	3.400	4.200	6.400	8.000

 Electrical Clearance in Substation:

Voltage	Height of I Bay From Ground (Mt)	Height of II Bay From Ground (Mt)	Bay Width (Mt)	Phase-Phase (Mt)	BetweenEquipment	Earth Wire From Ground
132KV (Single)	8.0	–	11.0	3.0	3.0	10.5
220KV (Single)	12.5	–	18	4.5	4.5	15.5
220KV (Double)	18.5	25	25	4.5	4.5	28.5
400KV	15.6	22	22.0	7.0	>6.0	30.0

Standard Bay Widths in Meters:

Voltage	Bay Width (Meter)
11KV	4.7 Meter
33KV	4.7 Meter
66KV	7.6 Meter
132KV	12.2 Meter
220KV	17 Meter
400KV	27 Meter

 Standard Bus and Equipment Elevation

Voltage	Equipment live Terminal Elevation (Meter)	Main Bus		Take of Elevation (Meter)
		Low	High
11 KV/33KV	2.8To 4	5.5  To6.5	9	6.5To8.5
66KV	2.8To 4	6To8	9To 10.5	9.5
132KV	3.7To5	8To9.5	13.5To14.5	12To12.5
220KV	4.9To5.5	9To13	18.5	15To18.5
400KV	8.0	15.5	–	23

 Phase spacing for strung Bus:

Voltage	Clearance
11KV	1300 mm
33KV	1300 mm
66KV	2200 mm
132KV	3000 mm
220KV	4500 mm
400KV	7000 mm

 Minimum Clearance of Live Parts from Ground:

Voltage	Minimum Clearance to Ground (Mt)	Section Clearance (Mt)
11KV	3.700	2.600
33KV	3.700	2.800
66KV	4.600	3.000
132KV	4.600	3.500
220KV	5.500	4.300
400KV	8.000	7.000

 Insulator String:

Voltage	No of Suspension String	Length (mm)	No of Disc for Tension String	Length in (mm)
66KV	5	965	6	1070
132KV	9	1255	10	1820
220KV	14	1915	15	2915
400KV	23	3850	2 X 23	5450

 Nominal Span:

Voltage	Normal Span (Meter)
66KV	240-250-275
132KV	315-325-335
220KV	315-325-335
400KV	315-325-335

 Minimum Ground Clearance:

Voltage	Ground (Meter)
66KV	5.5
132KV	6.1
220KV	7.0
400KV	8.0
800KV	12.4

 Indoor Substation Minimum Clearances

 

Distance	Descriptions
0.9 Meter	Horizontally between any item of equipment and thesubstation wall
0.6 Meter	Horizontally between any Two items of equipment
1.2 Meter	Horizontally in front of any HV switchgear

 Clearance of Conductor on Tower

Voltage	Tower Type	Vertical Space (Mt)	Horizontal Space(Mt)	Total Height From Ground(Mt)
66KV	A	1.03	4.0	15.91
	B	1.03	4.27	15.42
	C	1.22	4.88	16.24
132KV	A	7.140	2.17	23.14
	B	4.2	6.29	22.06
	C	4.2	7.15	22.68
	D	4.2	8.8	24.06
220KV	A	5.2	8.5	28.55
	B	5.25	10.5	29.08
	C	6.7	12.6	31.68
	D

 NORMS OF PROTECTION FOR EHV CLASS POWER TRANSFORMERS

Voltage ratio & capacity	HV Side	LV Side	Common relays
132/33/11KV up to 8 MVA	3 O/L relays + 1 E/L relay	2 O/L relays + 1 E/L relay	Buchholz, OLTC Buchholz, OT, WT
132/33/11KV above 8 MVA and below 31.5 MVA	3 O/L relays + 1 dir. E/L relay	3 O/L relays + 1 E/L relay	Differential, Buchholz, OLTC Buchholz, OT, WT
132/33KV, 31.5 MVA & above	3 O/L relays + 1 dir. E/L relay	3 O/L relays + 1 E/L relay	Differential, Over flux,Buchholz, OLTC PRV, OT, WT
220/33 KV, 31.5MVA & 50MVA 220/132KV, 100 MVA	3 O/L relays + 1 dir. E/L relay	3 O/L relays + 1 dir. relay	Differential, Over flux,Buchholz, OLTC PRV, OT, WT
400/220KV 315MVA	3 directional O/L relays (with dir. High set) +1 directional E/L relays. Restricted E/F relay + 3 Directional O/L relays for action	3 directional O/L relays (with dir. High set)+1 directional E/L relays. Restricted E/F relay	Differential, Over flux,Buchholz, OLTC PRV, OT, WT and overload (alarm) relay

 The bottom most portion of any insulator or bushing in service should be at a minimum height of 2500 mm above ground level.

 Location of L.A (From T.C Bushing):

Voltage	BIL KV Peak	Distance (Mt)
11KV	75	12
33KV	200	15
66KV	325	24
132KV	550	35
220KV	900 To 1050	Close To T.C
400KV	1425 To 1550